Access the videos through Speedgrader. This works exactly as it would for any Canvas assignment that accepts online submissions. In your Canvas course, go to Assignments, and click on the video assignment. If there are submissions, “Speedgrader” will appear at top right—click it.

Here you can toggle between students by clicking the current student’s name at top right. Each student’s playable video will appear in the lefthand submission panel, and you can submit comments and a grade in the righthand panel.